It is well-known that a backrest for a chair is so arranged that a spring fabric that makes an elastic deformation to expand and contract bridges between frames separately arranged at right and left sides as shown in the Japan Laid-Open Disclosure Public Patent Bulletin (Patent Laid-Open Number 10-192085). In accordance with the backrest, the spring fabric stretches to support a body of a seated person when a load of the seated person applies to the backrest. A feeling to sit on the chair can be adjusted to a certain degree by changing an initial tensile force of the spring fabric.
However, in a state that a load of the seated person is not applied, more specifically, in a state that no person sits on the chair, the spring fabric restores itself to a state that the spring fabric is strained between frames due to an elastic force. In other words, the spring fabric does not contribute to retaining a shape of a support face that supports the body of the seated person three dimensionally. This is inconvenient from a view point of appearance design of the chair.